The present invention relates to an optical semiconductor device and, for example, can be preferably used for an optical semiconductor device including various optical devices and electrical devices in a semiconductor chip.
Japanese Patent Laid-Open No. 2012-027198 (Patent Document 1) describes an optical semiconductor device including an optical waveguide that is a part of a semiconductor layer, a first impurity region which is formed in the semiconductor layer on one side of the optical waveguide and into which impurities of a first conductivity type are introduced, and a second impurity region which is formed in the semiconductor layer on the other side of the optical waveguide and into which impurities of a second conductivity type opposite to the first conductivity type are introduced. The optical semiconductor device includes a lower electrode that is a part of the second impurity region, an insulating film formed at least over the lower electrode, a capacitor including an upper electrode formed over the insulating film, and a third impurity region which is formed in the semiconductor layer at a part of a lower region of the upper electrode and into which the first conductivity type impurities are introduced.
In recent years, a technology in which optical signal transmission lines made of silicon are manufactured and an optical communication module is realized by integrating various optical devices and electronic devices using an optical circuit formed by the optical signal transmission lines as a platform, that is, a so-called silicon photonics technology, is actively developed. However, in the silicon photonics technology where various optical devices and electrical devices are included in a semiconductor chip, there is a problem that the quality of an electrical signal degrades due to effects of noise from a semiconductor substrate to an electrical signal transmission path.
The other purposes and new features will become clear from the description of the present specification and the accompanying drawings.
An optical semiconductor device according to an embodiment includes an insulating film over a semiconductor substrate, an optical waveguide of an optical signal transmission line formed from a semiconductor layer formed in a first region over the insulating film, a shielding semiconductor layer formed from the semiconductor layer formed in a second region over the insulating film, a multilayer wiring of n layers (n≧2), and an electrical signal transmission line formed by mth layer wiring (n≧m≧1) in the second region. The optical semiconductor device further includes a first noise cut wiring and a second noise cut wiring which are respectively formed on both sides of the electrical signal transmission line and which are formed from the mth layer wiring (n≧m≧1) that is away from and in parallel with the electrical signal transmission line, a first conductive portion that electrically couples the first noise cut wiring and the shielding semiconductor layer, and a second conductive portion that electrically couples the second noise cut wiring and the shielding semiconductor layer. In a cross-section perpendicular to an extending direction of the electrical signal transmission line, the electrical signal transmission line is surrounded by a shielding portion including the first noise cut wiring, the second noise cut wiring, the first conductive portion, the second conductive portion, and the shielding semiconductor layer, and the shielding portion is fixed to a reference potential.
According to an embodiment, it is possible to prevent the quality of an electrical signal from degrading in an optical semiconductor device.